> Isn't there a mental model that sooner or later they wouldn't be able to have returns higher than market returns

Reversion to the mean.

Also survivorship bias: at any given point there is a hotshot fund that outperforms the market, but fast forward five years and it's probably a different fund that did well, and the hotshot fund is underperforming the market, but nobody talks about them anymore.

All that matters is that there is a new golden child to fill financial news bandwith and get people shuffling their money around so the croupier gets paid.

Of course there are outliers like Rentech, but Cathie Wood is not Jim Simons.